Today, developers are focused more on providing all Internet Protocol (“IP”) solutions to roaming nodes (e.g., radios, telephones, laptops, personal digital assistants, etc.). As such, it is necessary to have a seamless IP-based mobility solution. Seamless mobility for mobile nodes from one location to another is hence becoming increasingly important. Thus, fast and reliable handoffs for the mobile node are becoming more important.
One of the ways to achieve low latency handoffs is to make use of layer 2 triggers to perform layer 3 handoffs. A pre-registration technique has been proposed in an Internet Draft to address low latency handoffs. The pre-registration technique exploits early triggers from the link layer that indicate a handoff is going to occur. The pre-registration technique uses this early trigger to start the mobile IP registration process from the mobile node's first foreign agent (i.e., current point of attachment), even though the registration itself is for a second foreign agent (i.e., new point of attachment). This early launch of the mobile IP registration process helps reduce overall handoff delay since more time is provided for the mobile IP registration to complete. As illustrated in FIG. 1, the first foreign agent 100 acts as a proxy for the second foreign agent 102 so that the mobile node 104 and the first foreign agent 100 can exchange messages on behalf of the second foreign agent 102. It is important to note that the first foreign agent does not generate the messages. The first foreign agent 100 simply relays the messages to and from the mobile node 104.
A disadvantage of the pre-registration technique as described in the Internet draft is that it relies on control signaling between the mobile node 104 and the first foreign agent 100 after the link layer has indicated that a handoff is imminent. In other words, the quality of the air interface link between the mobile node 104 and the first foreign agent 100 is likely deteriorating rapidly. The deterioration of the link between the mobile node 104 and the first foreign agent 100 increases the likelihood of dropped messages. Under these conditions, it may not always be possible for the mobile node 104 to complete the pre-registration process prior to the “link down” with the first foreign agent 100 (e.g., the mobile node 104 may be moving too fast). Under the Internet Draft, when pre-registration fails, the handoff time is longer than with standard mobile IP. This shortcoming makes the pre-registration techniques as described in the Internet draft less than desirable, especially for mission critical applications.
Further, in the case of a pre-registration failure, one of the following needs to occur before the mobile node 104 can perform a mobile IP registration: either the registration request timer expires and the mobile node 104 solicits another agent advertisement from the second foreign agent 102, or the second foreign agent 102 transmits its regular periodic agent advertisement. A disadvantage to this technique is that both of these events could take in the order of a second to occur, which would significantly slow the handoff process.
Alternatively, the mobile node 104 could always transmit an agent solicitation upon “link up” with the second foreign agent 102, and transmit a registration request to the home agent 106 upon receiving the advertisement. If the home agent 106 already has the care of address registered, the home agent 106 would simply refresh the state and send a reply. A disadvantage to this technique is that the number of registration requests could potentially double, which may lead to home agent 106 loading issues. Another disadvantage to this technique is wasted resources in case where the pre-registration succeeds.
Thus, there exists a need to perform certain enhancements to the mobile IP low latency handoffs in order to make it suitable for mission critical applications.